The present invention relates to a drive system for a motor vehicle and, more specifically, to a crash optimized bracket for removably affixing a propeller shaft to A motor vehicle.
There are generally four (4) main types of automotive drive line systems. More specifically, there exists a full-time front wheel drive system, a full-time rear wheel drive system, a part-time four wheel drive system, and an all-wheel drive system. Most commonly, the systems are distinguished by the delivery of power to different combinations of drive wheels, i.e., front drive wheels, rear drive wheels or some combination thereof. In addition to delivering power to a particular combination of drive wheels, most drive systems permit the respectively driven wheels to rotate at different speeds. For example, the outside wheels must rotate faster than the inside drive wheels, and the front drive wheels must normally rotate faster than the rear wheels.
Drive line systems also include one or more Cardan (Universal) and Constant Velocity joints (CVJ""s). Cardan joints are the most basic and common joint type used, for example, on propshafts. Although highly durable, Cardan joints are typically not suited for applications with high angles (e.g.  greater than 2 degrees) because of their inability to accommodate constant velocity rotary motion. Constant Velocity joints, in contrast, are well known in the art and are employed where transmission of a constant velocity rotary motion is desired or required. For example, a tripod joint is characterized by a bell-shaped outer race (housing) disposed around an inner spider joint which travels in channels formed in the outer race. The spider-shaped cross section of the inner joint is descriptive of the three equispaced arms extending therefrom which travel in the tracks of the outer joint. Part spherical rollers are featured on each arm.
One type of constant velocity universal joint is the plunging tripod type, characterized by the performance of end motion in the joint. Plunging tripod joints are currently the most widely used inboard (transmission side) joint in front wheel drive vehicles, and particularly in the propeller shafts found in rear wheel drive, all-wheel drive and 4-wheel drive vehicles. A common feature of tripod universal joints is their plunging or end motion character. Plunging tripod universal joints allow the interconnection shafts to change length during operation without the use of splines which provoke significant reaction forces thereby resulting in a source of vibration and noise.
The plunging tripod joint accommodates end wise movement within the joint itself with a minimum of frictional resistance, since the part-spherical rollers are themselves supported on the arms by needle roller bearings. In a standard ball roller type constant velocity joint the intermediate member of the joint (like the ball cage in a rzeppa constant velocity joint) is constrained to always lie in a plane which bisects the angle between the driving and driven shafts. Since the tripod type joint does not have such an intermediate member, the medium plane always lies perpendicular to the axis of the drive shaft.
Another common type of constant velocity universal joint is the plunging VL or xe2x80x9ccross groovexe2x80x9d type, which consists of an outer and inner race drivably connected through balls located in circumferentially spaced straight or helical grooves alternately inclined relative to a rotational axis. The balls are positioned in a constant velocity plane by an intersecting groove relationship and maintained in this plane by a cage located between the two races. The joint permits axial movement since the cage is not positionably engaged to either race. As those skilled in the art will recognize, the principal advantage of this type of joint is its ability to transmit constant velocity and simultaneously accommodate axial motion. Plunging VL constant velocity universal joints are currently used for high speed applications such as, for example, the propeller shafts found in rear wheel drive, all-wheel drive and 4-wheel drive vehicles.
The high speed fixed joint (HSFJ) is another type of constant velocity joint well known in the art and used where transmission of high speed is required. High speed fixed joints allow articulation to an angle (no plunge) but can accommodate much higher angles than with a Cardan joint or other non-CV joints such as, for example, rubber couplings. There are generally three types of high speed fixed joints: (1) disk style that bolts to flanges; (2) monoblock style that is affixed to the tube as a center joint in multi-piece propshafts; and (3) plug-on monoblock that interfaces directly to the axle or T-case replacing the flange and bolts.
A HSFJ generally comprises: (1) an outer joint member of generally hollow configuration, having a rotational axis and in its interior, a plurality of arcuate tracks circumferentially spaced about the axis extending in meridian planes relative to the axis, and forming lands between the tracks and integral with the outer joint part wherein the lands have radially inwardly directed surfaces; (2) an inner joint member disposed within the outer joint member and having a rotational axis, the inner joint member having on its exterior a plurality of tracks whose centerline lie in meridian planes with respect to the rotational axis of the inner joint member in which face the tracks of the outer joint member and opposed pairs, wherein lands are defined between the tracks on the inner joint member and have radially outwardly directed surfaces; (3) a plurality of balls disposed one in each pair of facing tracks in the outer and inner joint members for torque transmission between the members; and (4) a cage of annular configuration disposed between the joint members and having openings in which respective balls are received and contained so that their centers lie in a common plane, wherein the cage has external and internal surfaces each of which cooperate with the land surfaces of the outer joint member and inner joint member, respectively to locate the cage and the inner joint member axially.
In joints of this kind, the configuration of the tracks in the inner and outer joint members, and/or the internal and external surfaces of the cage are such that, when the joint is articulated, the common plane containing the centers of the balls substantially bisects the angle between the rotational axis of the joint members. As indicated above, there are several types of high speed fixed joints differing from one another with respect to the arrangement and configuration of the tracks in the joint members and/or to the internal and external surfaces of the cage whereby the common bisector plane is guided as described above thereby giving the joint constant-velocity-ratio operating characteristics. In each design, however, the cage is located axially in the joint by cooperation between the external cage surface and the surfaces of the lands facing the cages surface.
The outer surface of the cage and cooperating land surfaces of the outer joint member are generally spherical. When torque is transmitted by the joint, the forces acting in the joint cause the cage to be urged (by e.g. ball expulsion forces) towards one end of the joint which end will depend on the respective directions of the offsets of the tracks in the inner and outer joint members from the common plane when the joint is in its unarticulated position. To reduce the normal forces acting on the cage as a result of these ball expulsion forces, the amount of spherical wrap by the outer joint member lands is maximized for increased cage support.
In a disc-style constant velocity fixed joint, the outer joint member is open on both ends and the cage is assembled from the end opposite the end towards which the cage is urged by the ball expulsion forces under articulated load conditions. Assembly of the cage into the outer joint member is typically accomplished by either incorporating cage assembly notches into one of or a pair of lands in the outer joint member, or by sufficiently increasing the bore diameter of the outer joint part to allow the ball cage to be introduced into the outer joint part.
In a mono-block constant velocity fixed joint, also called a xe2x80x9cmono-block high speed fixed jointxe2x80x9d, the outer joint part is a bell-shaped member having a closed end. Accordingly, the cage must be assembled from the open end of the outer joint member. To accommodate assembly of the cage into the outer joint part, the bore diameter of the outer joint part must be sufficiently increased to allow assembly and/or assembly notches must be incorporated into at least one opposing pair of the outer joint member lands to allow introduction of the cage.
A typical driveline system incorporates one or more of the above joints to connect a pair of propeller shafts (front and rear) to a power take off unit and a rear driveline module, respectively. These propeller shafts (xe2x80x9cpropshaftsxe2x80x9d) function to transfer torque to the rear axle in rear wheel and all wheel drive vehicles. The propshafts are typically rigid in the axial directions and under certain circumstances, can contribute to the transfer of force down the fore-to-aft axis of the vehicle on impact, particularly in a frontal crash. Such transfer of energy can lead to high forces in the vehicle and thus high rates of acceleration for the occupants. Further, such energy can contribute to uncontrolled buckling of the propshaft itself resulting in damage to the passenger compartment or fuel tank from puncturing or the like.
Consequently, a need exists for an improved propeller shaft coupling which addresses and solves the aforementioned problems.
It is a principle object of the present invention to provide an improved bracket for removably affixing a propeller shaft to a motor vehicle.
It is a further object of the present invention to provide an improved bracket for removably affixing a propeller shaft to a motor vehicle which permits the propeller shaft to tear from the vehicle in a substantially downward direction during impact.
Still further, it is an object of the present invention to provide an improved bracket of the type discussed above which is tunable to allow a propeller shaft to decouple from a motor vehicle in a predictable manner in response to predetermined loads upon vehicle impact.
In carrying out the above objects there is provided a crash optimized bracket for removably coupling a propeller shaft or propeller shaft section center to a motor vehicle. The crash optimized bracket comprises an elongated member having a plurality of score lines or weakened slots that are preferably, but not necessarily, disposed vertically in a direction perpendicular to the length of the bracket. In a preferred embodiment, the slots are disposed in predetermined locations with predetermined weaknesses so as to allow the bracket to tear in a predictable and controlled manner in a generally downward direction upon impact. Such placement, arrangement, and weakness setting permits the bracket and thus the corresponding propeller shaft or propeller shaft section to be tuned to respond to predetermined loads.
In a preferred embodiment, the crash optimized bracket comprises a generally elongated member having a variable thickness across its length. The thickness may be greater in the middle and substantially thinner at each end. It is understood, however, that any suitable shape, length or thickness may be utilized depending upon the particular application.
These and other objects features and advantages of the present invention will become more readily apparent with reference to the following detailed description of the invention wherein like reference numerals correspond to like components.